1. Field of the Invention
The present invention relates to an ink supply method for supplying ink to an ink container and a printing apparatus using the ink supply method. In particular, the present invention relates to an ink supply method for supplying ink by using a gas-liquid separation member that permits gas to pass therethrough and that prevents liquid from passing therethrough and a printing apparatus.
2. Description of the Related Art
One of conventional ink jet printing apparatuses is shown in FIG. 9. This ink jet printing apparatus is a serial scan-type printing apparatus in which a printing operation is performed by moving a printing head 1 on a printing medium in a main scanning direction of an arrow X while the printing head 1 is guided by a guide axis 8. This method as shown in FIG. 9 is a so-called head cartridge method that is one of methods for supplying ink to the printing head 1. In this head cartridge method, a head cartridge 1b is composed of the printing head 1 including a nozzle that can eject ink; and a main tank 4 for storing ink to be supplied to the printing head 1. This method provides printing and scanning operations by moving a carriage 1a having the head cartridge 1b along a guide axis 8 in the main scanning direction.
Another method for supplying ink to the printing head 1 is a tank cartridge method as shown in FIG. 10. According to this method, the printing head 1 is mounted on the carriage 1a and a tank cartridge 1c for storing ink to be supplied to the printing head 1 is provided at the body of the printing apparatus. Ink is supplied from the tank cartridge 1c to the printing head 1 via a flexible ink supply tube 1d connecting the printing head 1 to the tank cartridge c. 
However, the former head cartridge method mounts the head cartridge 1b including the ink tank 4 on the carriage 1a and thus the carriage 1a has a high laden weight. This prevents the carriage 1a from moving with a high speed. Furthermore, when the head cartridge 1b has a reduced size in order to reduce the laden weight of the carriage 1a, the ink tank 4 has a reduced capacity, causing a reduced number of printable printing media. In the case of the latter tank cartridge method, the ink cartridge 1c at the printing apparatus body is connected to the printing head 1 at the carriage 1a via the ink supply tube 1d, which causes a complicated ink supply mechanism to make it difficult to reduce the size of the printing apparatus.
In order to solve the inconveniences of the conventional ink supply methods as described above, the so-called pit-in method has been considered. This supply method is used in the serial scan type printing apparatus as described above so that a printing head and a sub tank having a relatively small capacity are mounted on a carriage and a main tank having a relatively large capacity is provided at the body of the printing apparatus. The sub tank is a tank for storing ink to be supplied to the printing head and is supplied with ink from the main tank when the sub tank and the carriage are moved to a predetermined home position. Specifically, when the carriage is moved to the home position, an ink supply section of the sub tank is connected with a joint of the main tank to form an ink supply path. Then, ink is supplied from the main tank to the sub tank by using a negative pressure generating unit to decompress the interior of the sub tank.
The pit-in method as described above uses a sub tank having a small capacity mounted on a carriage and thus a laden weight on the carriage can be reduced, thus allowing the printing head to perform printing and scanning with a high speed. Furthermore, the ink supplied from the main tank to the sub tank at the home position can increase the number of printing media to be printed. Furthermore, the pit-in method does not require the carriage to be connected to the tank via an ink supply tube as in the tank cartridge method of FIG. 10, thus simplifying the structure of the apparatus.
With regards to the pit-in type ink jet printing apparatus as described above, a method has been disclosed for controlling an ink supply system by using a sensor to detect an ink amount that can be supplied to the subtank when the carriage is moved to the home position as a mechanism for replenishing ink from the main tank to the sub tank (see Japanese Patent Application Laid-open No. 08-112913 (1996)). However, the control of the ink amount using the sensor as described above is complicated, thus causing the resultant apparatus to have an increased price.
From the viewpoint as described above, a pit-in type ink jet printing apparatus has been suggested in which a sub tank includes a gas-liquid separation member to simplify the control of an ink supply amount (see Japanese Patent Application Laid-open No. 2004-181952).
FIG. 5 is a schematic cross sectional view of a printing head in the pit-in type ink jet printing apparatus as described above. FIG. 6 is a cross-sectional view taken along the line VI-VI of FIG. 5.
A printing head of this example includes a sub tank 3 and an ink jet printing element 38. This printing head is mounted on a carriage of a serial scan-type ink jet printing apparatus. An ink reservoir portion R of the sub tank 3 includes an ink absorption member 37. An ink reservoir portion-constituting member 35 is attached with a gas-liquid separation member 33 that is positioned at a boundary between an exhaust path 36 and the ink reservoir portion R. The gas-liquid separation member 33 is a member that allows gas to pass therethrough but blocks liquid such as ink. The gas-liquid separation member 33 is a porous film formed by PTFE having a thickness of about several tens micrometers for example. The ink reservoir portion R is divided into the three sections as shown in FIG. 6 and the respective sections store different colors of inks. The ink jet printing element 38 includes ink ejection openings that can eject these inks.
At the boundary between the three ink reservoir portions R and the exhaust path 36 common to them, the one gas-liquid separation member 33 is positioned. The gas-liquid separation member 33 is heat-deposited with the inner side of a rib 35A formed at the outer periphery of the ink reservoir portion-constituting member 35. The three ink reservoir portions R are separated from one another and the top part thereof and the one exhaust path 36 have therebetween the one gas-liquid separation member 33. The reference numeral 34 denotes a member constituting the exhaust path.
When ink is supplied from the main tank to the sub tank 3, the carriage is moved to the home position. The main tank stores therein the respective inks to be supplied to the respective ink reservoir portions R. As shown in FIG. 5, an ink ejection opening of the ink jet printing element 38 is sealed by a dummy cap 6 and ink supply openings 11 of the respective ink reservoir portions R are connected to the corresponding respective Joints 10 of the main tank. An suction cap 22 of the body of the printing apparatus is also connected to a vent hole 15 of the sub tank 3. Then, a negative pressure generating unit included in the printing apparatus is activated to exhaust air in the respective ink reservoir portions R via the gas-liquid separation member 33, the exhaust path 36, the vent hole 15, and the suction cap 22. This decompresses the interior of the respective ink reservoir portions R to allow the respective corresponding colors of ink to be supplied from the main tank into the respective ink reservoir portions R via the respective joints 10, the respective ink supply openings 11, and the respective ink supply paths 12. When the interior of the ink reservoir portion R is filled with ink and the fluid level of the ink reaches the gas-liquid separation member 33, the gas-liquid separation member 33 will automatically stop the supply of ink. Thus, the respective ink reservoir portions R can be automatically supplied with ink until they are filled with the corresponding inks without requiring a special control of an amount of supplied ink.
Thus, by setting an air intake amount of the negative pressure generating unit to be equal to or higher than the total of the inner volumes of the respective ink reservoir portions R, air in the respective ink reservoir portions R is exhausted, regardless of the amount of ink left in the respective ink reservoir portions R, via the gas-liquid separation member 33 to subsequently supply ink to the respective ink reservoir portions R until they are filled up with ink. In this manner, the respective ink reservoir portions R can be filled up with ink by exhausting air in an amount equal to or higher than a predetermined amount from the respective ink reservoir portions R. Thus, control of air exhaust is not required and thus the negative pressure generating unit can be designed with a sufficient margin.
In the structure according to the pit-in method of FIG. 6, the interior of the sub tank 3 is divided into the three ink reservoir portions R and the one gas-liquid separation member 33 is deposited, in order to improve the assembly, with the inner side of the rib 35A formed at the outer periphery of the ink reservoir portion-constituting member 35 so as to divide the respective ink reservoir portions R from one another. Thus, the ink reservoir portion R has a vacant region 16 having no ink absorption member 37 that is provided between the ink absorption member 37 and the gas-liquid separation member 33.
FIG. 7 and FIG. 8 illustrate the condition just before the ink reservoir portion R is filled up with ink by an ink refill in the pit-in method as described above.
When the air in the ink reservoir portion R is exhausted from the vent hole 15 via the gas-liquid separation member 33, the interior of the ink reservoir portion R is gradually filled with ink from the lower part to the upper part in the gravitational direction of the ink absorption member 37. When ink reaches the vacant region 16 of the ink absorption member, ink is instantaneously filled to the region 16 because the region 16 does not have the ink absorption member 37. Then, as shown in a part 17R in FIG. 7 and FIG. 8, ink is finally filled at a predetermined point in the gas-liquid separation member 33.
The part 17R to which ink is finally filled as described above represents a position at which a very high pressure called water hammer is applied to the gas-liquid separation member 33 when air passes through the gas-liquid separation member 33. The part at which the phenomenon as described above is caused will be called as “defoaming point” for convenience. When an ink supply to the ink reservoir portion R is repeated, a risk may be caused in which a high pressure caused at the defoaming point 17R deteriorates the gas-liquid separation capability of the gas-liquid separation member 33 at the defoaming point 17R. Thus, the defoaming point 17R is also a damage point of the gas-liquid separation member 33. When the gas-liquid separation capability of the gas-liquid separation member 33 is decreased, a risk may be caused in which ink gradually leaks from the gas-liquid separation member 33 to the exhaust path 36. The position of the defoaming point 17R as described above is positioned almost at the center of the ventilation face 18 of the gas-liquid separation member 33 positioned in the ink reservoir portion R. However, the position of the defoaming point 17R is slightly different depending on the shape of the ink reservoir portion R.
When the gas-liquid separation capability of the gas-liquid separation member 33 is decreased, a risk may be caused in which a large amount of ink leaks to the exhaust path 36 to deteriorate the air permeability of the gas-liquid separation member 33 to prevent ink from being supplied properly. When ink leaks from the air inlet 15 to outside, a risk may be caused in which the interior of the ink jet printing apparatus is soiled or a printing medium is soiled during a printing operation.